This invention relates to an IC tag incorporating therein an IC chip operable by radio waves, and also to a method for fabricating such an IC tag.
RFID (radio frequency identification) tags have recently come to be widely used in such a way that they are attached to commercial articles, IC cards, etc. so as to control the information on the articles. Such an IC tag mainly consists of an IC chip and an antenna. An external reader/writer can communicate with the IC chip by using radio waves radiated from the antenna so that the reader/writer can interpret such information as ID (identification) data stored in the IC chip. Thus, the data stored in the IC chip can be read out, or additional data can be written in the IC chip, in a non-contact manner, i.e. without any physical contact between the reader/writer and the IC tag.
For example, in one of widely known applications, RFID tags in which specific information is written are attached to commercial articles; a reader/writer reads out the information from or writes other information in, the RFID tags during the process of fabricating or transporting the articles; and the information on the articles provided during the process is administered. The reader/writer mentioned above is so designed as to be able to read out the information as a whole stored in the IC chip of the RFID tag located within an area in which the reader/writer can communicate with the RFID tag. Thus, the RFID tags can improve the efficiency of information administration.
There, however, is a problem with this useful application of the RFID tag. To illustrate such a problematic example, let it be assumed that envelopes are administered by the use of RFID tags. RFID tags are normally stuck at almost the same positions on the envelopes and if these envelopes are piled up one upon another, those RFID tags are also piled up one upon another, with one tag located very closely to another. This close existence of plural RFID tags gives rise to the change in the impedance of the antenna of each RFID tag and to the interference between the radio waves radiated from the antennas of the RFID tags. Consequently, the reader/writer fails to properly read out the information stored in the RFID tags.
To solve such a problem as described above, a technical measure has been proposed wherein a spacer is interposed between two piled RFID tags, the thickness of the spacer being larger than a specific distance at or beyond which the radio waves radiated from the antennas of the two piled RFID tags do not interfere with each other. Reference should be made to, for example, Japanese patent document JP-A-2005-001692, paragraphs 0016 through 0019, FIGS. 1 and 2.